The crystal structure of the acid protease from Rhizopus chinensis has been refined to 1.8 angstrom resolution and the nature of its interaction with pepstatin further defined. Synchrotron radiation data have been collected on a parent and one heavy atom derivative of creatine kinase. Neutron and X-ray data have been collected on a complex of ribonuclease with uridine vanadate, transition state analog. Neutron data have been collected on crystals of insulin.